1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Dynamic function tracer architecture backend. 4 * 5 * Copyright IBM Corp. 2009,2014 6 * 7 * Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com> 8 */ 9 10 #include <linux/hardirq.h> 11 #include <linux/uaccess.h> 12 #include <linux/ftrace.h> 13 #include <linux/kernel.h> 14 #include <linux/types.h> 15 #include <linux/kmsan-checks.h> 16 #include <linux/kprobes.h> 17 #include <linux/execmem.h> 18 #include <trace/syscall.h> 19 #include <asm/asm-offsets.h> 20 #include <asm/text-patching.h> 21 #include <asm/cacheflush.h> 22 #include <asm/ftrace.lds.h> 23 #include <asm/nospec-branch.h> 24 #include <asm/set_memory.h> 25 #include "entry.h" 26 #include "ftrace.h" 27 28 /* 29 * To generate function prologue either gcc's hotpatch feature (since gcc 4.8) 30 * or a combination of -pg -mrecord-mcount -mnop-mcount -mfentry flags 31 * (since gcc 9 / clang 10) is used. 32 * In both cases the original and also the disabled function prologue contains 33 * only a single six byte instruction and looks like this: 34 * > brcl 0,0 # offset 0 35 * To enable ftrace the code gets patched like above and afterwards looks 36 * like this: 37 * > brasl %r0,ftrace_caller # offset 0 38 * 39 * The instruction will be patched by ftrace_make_call / ftrace_make_nop. 40 * The ftrace function gets called with a non-standard C function call ABI 41 * where r0 contains the return address. It is also expected that the called 42 * function only clobbers r0 and r1, but restores r2-r15. 43 * For module code we can't directly jump to ftrace caller, but need a 44 * trampoline (ftrace_plt), which clobbers also r1. 45 */ 46 47 void *ftrace_func __read_mostly = ftrace_stub; 48 struct ftrace_insn { 49 u16 opc; 50 s32 disp; 51 } __packed; 52 53 #ifdef CONFIG_MODULES 54 static char *ftrace_plt; 55 #endif /* CONFIG_MODULES */ 56 57 static const char *ftrace_shared_hotpatch_trampoline(const char **end) 58 { 59 const char *tstart, *tend; 60 61 tstart = ftrace_shared_hotpatch_trampoline_br; 62 tend = ftrace_shared_hotpatch_trampoline_br_end; 63 #ifdef CONFIG_EXPOLINE 64 if (!nospec_disable) { 65 tstart = ftrace_shared_hotpatch_trampoline_exrl; 66 tend = ftrace_shared_hotpatch_trampoline_exrl_end; 67 } 68 #endif /* CONFIG_EXPOLINE */ 69 if (end) 70 *end = tend; 71 return tstart; 72 } 73 74 bool ftrace_need_init_nop(void) 75 { 76 return true; 77 } 78 79 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec) 80 { 81 static struct ftrace_hotpatch_trampoline *next_vmlinux_trampoline = 82 __ftrace_hotpatch_trampolines_start; 83 static const char orig[6] = { 0xc0, 0x04, 0x00, 0x00, 0x00, 0x00 }; 84 static struct ftrace_hotpatch_trampoline *trampoline; 85 struct ftrace_hotpatch_trampoline **next_trampoline; 86 struct ftrace_hotpatch_trampoline *trampolines_end; 87 struct ftrace_hotpatch_trampoline tmp; 88 struct ftrace_insn *insn; 89 const char *shared; 90 s32 disp; 91 92 BUILD_BUG_ON(sizeof(struct ftrace_hotpatch_trampoline) != 93 SIZEOF_FTRACE_HOTPATCH_TRAMPOLINE); 94 95 next_trampoline = &next_vmlinux_trampoline; 96 trampolines_end = __ftrace_hotpatch_trampolines_end; 97 shared = ftrace_shared_hotpatch_trampoline(NULL); 98 #ifdef CONFIG_MODULES 99 if (mod) { 100 next_trampoline = &mod->arch.next_trampoline; 101 trampolines_end = mod->arch.trampolines_end; 102 shared = ftrace_plt; 103 } 104 #endif 105 106 if (WARN_ON_ONCE(*next_trampoline >= trampolines_end)) 107 return -ENOMEM; 108 trampoline = (*next_trampoline)++; 109 110 /* Check for the compiler-generated fentry nop (brcl 0, .). */ 111 if (WARN_ON_ONCE(memcmp((const void *)rec->ip, &orig, sizeof(orig)))) 112 return -EINVAL; 113 114 /* Generate the trampoline. */ 115 tmp.brasl_opc = 0xc015; /* brasl %r1, shared */ 116 tmp.brasl_disp = (shared - (const char *)&trampoline->brasl_opc) / 2; 117 tmp.interceptor = FTRACE_ADDR; 118 tmp.rest_of_intercepted_function = rec->ip + sizeof(struct ftrace_insn); 119 s390_kernel_write(trampoline, &tmp, sizeof(tmp)); 120 121 /* Generate a jump to the trampoline. */ 122 disp = ((char *)trampoline - (char *)rec->ip) / 2; 123 insn = (struct ftrace_insn *)rec->ip; 124 s390_kernel_write(&insn->disp, &disp, sizeof(disp)); 125 126 return 0; 127 } 128 129 static struct ftrace_hotpatch_trampoline *ftrace_get_trampoline(struct dyn_ftrace *rec) 130 { 131 struct ftrace_hotpatch_trampoline *trampoline; 132 struct ftrace_insn insn; 133 s64 disp; 134 u16 opc; 135 136 if (copy_from_kernel_nofault(&insn, (void *)rec->ip, sizeof(insn))) 137 return ERR_PTR(-EFAULT); 138 disp = (s64)insn.disp * 2; 139 trampoline = (void *)(rec->ip + disp); 140 if (get_kernel_nofault(opc, &trampoline->brasl_opc)) 141 return ERR_PTR(-EFAULT); 142 if (opc != 0xc015) 143 return ERR_PTR(-EINVAL); 144 return trampoline; 145 } 146 147 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, 148 unsigned long addr) 149 { 150 struct ftrace_hotpatch_trampoline *trampoline; 151 u64 old; 152 153 trampoline = ftrace_get_trampoline(rec); 154 if (IS_ERR(trampoline)) 155 return PTR_ERR(trampoline); 156 if (get_kernel_nofault(old, &trampoline->interceptor)) 157 return -EFAULT; 158 if (old != old_addr) 159 return -EINVAL; 160 s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr)); 161 return 0; 162 } 163 164 static int ftrace_patch_branch_mask(void *addr, u16 expected, bool enable) 165 { 166 u16 old; 167 u8 op; 168 169 if (get_kernel_nofault(old, addr)) 170 return -EFAULT; 171 if (old != expected) 172 return -EINVAL; 173 /* set mask field to all ones or zeroes */ 174 op = enable ? 0xf4 : 0x04; 175 s390_kernel_write((char *)addr + 1, &op, sizeof(op)); 176 return 0; 177 } 178 179 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, 180 unsigned long addr) 181 { 182 /* Expect brcl 0xf,... */ 183 return ftrace_patch_branch_mask((void *)rec->ip, 0xc0f4, false); 184 } 185 186 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) 187 { 188 struct ftrace_hotpatch_trampoline *trampoline; 189 190 trampoline = ftrace_get_trampoline(rec); 191 if (IS_ERR(trampoline)) 192 return PTR_ERR(trampoline); 193 s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr)); 194 /* Expect brcl 0x0,... */ 195 return ftrace_patch_branch_mask((void *)rec->ip, 0xc004, true); 196 } 197 198 int ftrace_update_ftrace_func(ftrace_func_t func) 199 { 200 ftrace_func = func; 201 return 0; 202 } 203 204 void arch_ftrace_update_code(int command) 205 { 206 ftrace_modify_all_code(command); 207 } 208 209 void ftrace_arch_code_modify_post_process(void) 210 { 211 /* 212 * Flush any pre-fetched instructions on all 213 * CPUs to make the new code visible. 214 */ 215 text_poke_sync_lock(); 216 } 217 218 #ifdef CONFIG_MODULES 219 220 static int __init ftrace_plt_init(void) 221 { 222 const char *start, *end; 223 224 ftrace_plt = execmem_alloc(EXECMEM_FTRACE, PAGE_SIZE); 225 if (!ftrace_plt) 226 panic("cannot allocate ftrace plt\n"); 227 228 start = ftrace_shared_hotpatch_trampoline(&end); 229 memcpy(ftrace_plt, start, end - start); 230 set_memory_rox((unsigned long)ftrace_plt, 1); 231 return 0; 232 } 233 device_initcall(ftrace_plt_init); 234 235 #endif /* CONFIG_MODULES */ 236 237 #ifdef CONFIG_FUNCTION_GRAPH_TRACER 238 /* 239 * Hook the return address and push it in the stack of return addresses 240 * in current thread info. 241 */ 242 unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp, 243 unsigned long ip) 244 { 245 if (unlikely(ftrace_graph_is_dead())) 246 goto out; 247 if (unlikely(atomic_read(¤t->tracing_graph_pause))) 248 goto out; 249 ip -= MCOUNT_INSN_SIZE; 250 if (!function_graph_enter(ra, ip, 0, (void *) sp)) 251 ra = (unsigned long) return_to_handler; 252 out: 253 return ra; 254 } 255 NOKPROBE_SYMBOL(prepare_ftrace_return); 256 257 /* 258 * Patch the kernel code at ftrace_graph_caller location. The instruction 259 * there is branch relative on condition. To enable the ftrace graph code 260 * block, we simply patch the mask field of the instruction to zero and 261 * turn the instruction into a nop. 262 * To disable the ftrace graph code the mask field will be patched to 263 * all ones, which turns the instruction into an unconditional branch. 264 */ 265 int ftrace_enable_ftrace_graph_caller(void) 266 { 267 int rc; 268 269 /* Expect brc 0xf,... */ 270 rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa7f4, false); 271 if (rc) 272 return rc; 273 text_poke_sync_lock(); 274 return 0; 275 } 276 277 int ftrace_disable_ftrace_graph_caller(void) 278 { 279 int rc; 280 281 /* Expect brc 0x0,... */ 282 rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa704, true); 283 if (rc) 284 return rc; 285 text_poke_sync_lock(); 286 return 0; 287 } 288 289 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ 290 291 #ifdef CONFIG_KPROBES_ON_FTRACE 292 void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, 293 struct ftrace_ops *ops, struct ftrace_regs *fregs) 294 { 295 struct kprobe_ctlblk *kcb; 296 struct pt_regs *regs; 297 struct kprobe *p; 298 int bit; 299 300 if (unlikely(kprobe_ftrace_disabled)) 301 return; 302 303 bit = ftrace_test_recursion_trylock(ip, parent_ip); 304 if (bit < 0) 305 return; 306 307 kmsan_unpoison_memory(fregs, sizeof(*fregs)); 308 regs = ftrace_get_regs(fregs); 309 p = get_kprobe((kprobe_opcode_t *)ip); 310 if (!regs || unlikely(!p) || kprobe_disabled(p)) 311 goto out; 312 313 if (kprobe_running()) { 314 kprobes_inc_nmissed_count(p); 315 goto out; 316 } 317 318 __this_cpu_write(current_kprobe, p); 319 320 kcb = get_kprobe_ctlblk(); 321 kcb->kprobe_status = KPROBE_HIT_ACTIVE; 322 323 instruction_pointer_set(regs, ip); 324 325 if (!p->pre_handler || !p->pre_handler(p, regs)) { 326 327 instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE); 328 329 if (unlikely(p->post_handler)) { 330 kcb->kprobe_status = KPROBE_HIT_SSDONE; 331 p->post_handler(p, regs, 0); 332 } 333 } 334 __this_cpu_write(current_kprobe, NULL); 335 out: 336 ftrace_test_recursion_unlock(bit); 337 } 338 NOKPROBE_SYMBOL(kprobe_ftrace_handler); 339 340 int arch_prepare_kprobe_ftrace(struct kprobe *p) 341 { 342 p->ainsn.insn = NULL; 343 return 0; 344 } 345 #endif 346